A) Field of the Invention
This invention relates to a solid state imaging apparatus, and more in detail, relates to a driving method of the solid state imaging apparatus.
B) Description of the Related Art
FIG. 10 is a schematic plan view showing a conventional solid-state imaging apparatus 51.
The solid-state imaging apparatus 51 is consisted of a light-receiving region 62 including a plurality of photoelectric conversion elements 52 and a vertical signal electric charge transfer device (a vertical charge coupled device: VCCD) transferring the signal electric charges generated by the photoelectric conversion elements 52, a horizontal signal electric charge transfer device (a horizontal charge coupled device: HCCD) 73 transferring the signal electric charges transferred by the VCCD 54 to a horizontal direction and an output amplifier 74.
The light-receiving region 62 in the imaging device adopting the pixel interleaved array CCD (PIACCD) as shown in the drawing is consisted of the plurality of the photoelectric conversion elements that are configured in a pixel interleaved arrangement. Between each row of the photoelectric conversion elements, a vertical electric charge transfer device 64 which reads the signal electric charges generated by the photoelectric conversion elements 52 and transfers them to a vertical direction are arranged by traversing in the spaces among the photoelectric conversion elements 52 in the vertical direction. Transfer channels are positioned in the zigzag spaces formed by the pixel interleaved arrangement, and the adjacent transfer channels apart from each other via the photoelectric conversion elements and come closer to each other via the channel stop region 53. For example, the details of the pixel interleaved arrangement can be found in Japanese Laid-Open Patent Hei 10-136391 and Tetsuo Yamada, et al, February, 2000, “A Progressive Scan CCD Imager for DSC Applications”, ISSCC Digest of Technical Papers, Page 110 to 111.
The vertical electric charge transfer device 64 is consisted of the vertical transfer channel 54 shown in FIG. 11A and in FIG. 11B and transfer electrodes 16a and 16b which are formed over the vertical transfer channel 54 via an insulating film 10a and wobbling the photoelectric conversion elements 52 to the horizontal direction.
FIG. 11A is an enlarged plan view showing a part of the light receiving region 52 in the conventional solid-state imaging apparatus 51. FIG. 9B is an enlarged cross sectional view showing the conventional solid-state imaging apparatus 51 cut across a broken line A-B in FIG. 11A.
Each of the vertical transfer channel 54 is formed corresponding to each row of the photoelectric conversion elements 52, and transfers the signal electric charges read out via a reading-out gate channel region 51c formed adjoining to each photoelectric conversion element 52 to the vertical direction. A channel stop region 53 is positioned adjoining to the vertical transfer channel 54 on the opposite side of the reading-out gate channel region 51c. Moreover, the transfer electrodes 56 (the first layer poly-silicon electrode 56a and the second layer poly-silicon 56b) are formed over the vertical transfer channel 54 via the insulating film 60a. Furthermore, at the cross section of this part, only the second layer poly-silicon electrode 56b is positioned over the vertical transfer channel 54. Further, the conventional solid-state imaging apparatus 51 has a structure wherein the two vertical transfer channels 54 are adjoining via the channel stop regions 53.
During a reading-out period, the signal charges generated by the photoelectric conversion elements (pixel) 52 are read out to the vertical transfer channels by imposing a high level voltage (VH) to the first layer poly-silicon electrode 56b (φV1) or 56d (φV3) equipped on the reading-out gate channel region (reading-out part) 51c. 
Thereafter, during a transfer period, the signal charges are transferred to the HCCD 73 by sequentially imposing a mid-level pulse (VM) or a low-level pulse (VL) to the transfer electrodes 56a to 56d. A horizontal transfer of the electric charges by the HCCD 73 is executed by the two-phase drive with HM/HL pulses during a period between the transfer operations of the VCCD 64 in the transfer period.
FIG. 12 shows electric potentials between a broken line E-F in FIG. 9B. An overflow drain that discharges an excessive signal electric charge of the photoelectric conversion elements 52 is formed by adding an inverse bias on an n-type substrate 51a to form an appropriate electric potential barrier between the photoelectric conversion element 52 and the n-type substrate 51a. 
In the drawing, the electric potential indicated with a solid line is in a condition that the electric charges are accumulated in the photoelectric conversion element 52. Since a low voltage (VM or VL) is imposed on the electrode 56b, a reading part 51c is closed, and the accumulated signal charges are not read out to the vertical transfer channel 54.
In the drawing, the electric potential indicated with a dashed line is in a condition that a high voltage (VH) is imposed on the electrode 56b, and the electric potential barrier to the vertical transfer channel 54 from the photoelectric conversion elements 52 is eliminated by imposing a sufficient high voltage, and all the electric charges will move to the vertical transfer channel 54. Moreover, two vertical transfer channels 54 which are adjacent via the channel stop region 53 become high electric potential, although the channel stop region 53 divides them. Since the signal electric charges are accumulated in the vertical transfer channel 54 which is adjacent to the reading part 51c at the reading-out period, the signal charges that can be accumulated in the vertical channel 54 in terms of electric potential will not exceed the electric potential of the channel stop region 53.
FIG. 13A is a timing chart showing driving waveforms imposed on electrodes V1 to V4 consisted of the electrode 56a and the electrode 56b in the conventional solid-state imaging apparatus 51. This timing chart is indicated by peak values of VH, VM and VL. VH is a voltage at the reading-out period, and change in VM and VL relates to the operation in the transfer period. FIG. 13B is a schematic view representing conditions of the electric potentials of the vertical transfer channel 54 and movements of the signal electric charges when the driving waveforms shown in FIG. 13A are imposed. In the drawing, a white square indicates VL, a hatched square indicates VM and a black square indicates VH, and a hatched circle indicates the signal electric charges. The signal electric charges can be accumulated in the vertical transfer channel 54 when VM is imposed, and the vertical transfer channel 54 will be potential barrier when VL is imposed. At a timing t1, the signal electric charges are accumulated in the photoelectric conversion elements 52. At a timing t3, the VH is imposed on reading electrodes V1 and the signal electric charges are moved from the photoelectric conversion elements 52 in every two lines in the vertical direction to the vertical transfer channel 54. At a timing t5, the signal electric charges are moved from the photoelectric conversion elements 52 in the remaining every two lines in vertical direction to the vertical transfer channel 54. At a timing t7, the signal electric charges are accumulated under the electrodes V2 and V3, and the transfer period will start in this condition.
FIG. 14 is an enlarged plan view showing a part enclosed with a double short-dashed line in FIG. 11A. In the drawing, S2 indicates a region of a channel formed by the electrode 56b at the reading-out period. An accumulation capacity at the reading-out period is decided approximately by a difference φa between the electric potential of the vertical transfer channel 54 that is adjoining to the reading part 51c shown in FIG. 12 and the electric potential barrier of the channel stop region 53 and an area of the S2 and a static capacity for the area per unit (the maximum accumulation capacity equals to or approximately equals to αS2φa, when α is the static capacity for the area per unit).
In a case that this maximum accumulation capacity is smaller than the maximum accumulation capacity of the photoelectric conversion element 52, the signal electric charges flow into an adjacent vertical transfer channel 54m over the electric potential barrier of the channel stop region 53, and it causes a blooming phenomenon that will deteriorate an image of a blight part as the solid-state imaging apparatus. That is, the dynamic range will be lost as a reduction of the dealing signal amount. Moreover, this blooming phenomenon is appeared at the timings t3 and t5 in FIG. 13B.